EPI T/E 320 Speaker System Review
The design of conventional loudspeaker diaphragms (cones or domes) has always been a series of compromises. The ideal diaphragm must strike the proper balance between lightness, stiffness, and internal damping (the property that prevents a material from resonating while it vibrates). EPI's Time/Energy series of loudspeakers addresses this classic standoff with several newly designed drivers.
All of the new drivers are meant to have good time/energy response. EPI describes this property as the ability to reproduce short pulses accurately by virtue of using stiff yet well-damped diaphragms that respond rapidly to transients, that do not store mechanical energy and release it as sound after the signal has ended.
Finding that no single material commonly used in speaker diaphragms had all the necessary properties for good time/energy response, the EPI engineers decided to use layered materials. The foam-plastic midrange and woofer cones are formed integrally with their edge suspensions in a single structure, each diaphragm having a contour and profile optimized for its function. The foam material provides the necessary self-damping qualities.
For stiffness, a clear, light, and rather rigid plastic cone is bonded to the outside of the foam cone to form a single rigid structure with the desired mechanical properties.
The tweeter diaphragm and its integral surround suspension are also made of plastic foam, but the outer-surface coating is applied by a spraying process instead of bonding. The two-layer construction was found to adversely affect the high-frequency response of the concave dome tweeter shape that has been used in EPI speakers for many years. A new, more conventional-looking convex dome shape was developed to exploit the advantages of the new materials while retaining or surpassing the high-frequency performance of the older driver.
The T/E series presently consists of six models; the T/E 320 tested in this report is the next-to-largest model in the line. It is a three-way floor-standing system with a 10-inch woofer crossing over at 700 Hz to a 4-inch midrange driver, which in turn crosses over to a 1-inch dome tweeter at 3,000 Hz. The enclosure measures 29 x 17 x 10-1/2 inches and weighs 52 pounds. The cabinet is covered with walnut-grain vinyl veneer and has a snap-on grille of acoustically transparent brown cloth. Recessed into the rear of the cabinet are insulated connectors accepting stripped speaker cable. There are no external controls. Price: $250 each.
The quasi-anechoic frequency response of the EPI T/E 320, measured at a 1-meter distance with our IQS FFT-analysis system, showed some midrange fluctuations that appeared to be caused by refraction at the cabinet edges or other interference effects (the overall range of output variation was about 6 dB at several points between 1,000 and 6,000 Hz). From 8,000 to 18,000 Hz, the response was very smooth and varied about 4 dB overall. A close-miked measurement of mid-range-driver output showed a definite notch at the 3,000-Hz crossover to the tweeter, but this was not visible in our other measurements.
The room response of the EPI T/E 320 (measured at the far end of the room and using a swept sine-wave driving signal and averaging the outputs of both speakers) was quite smooth over most of its range, with an overall variation of about 5 dB from 370 to 20,000 Hz. At lower frequencies, the speaker's characteristics were obscured by room resonances, so we measured the woofer response separately, with close microphone spacing, and "spliced" the two curves together. The woofer output varied only 3 dB overall from 40 to 400 Hz, with a broad maximum in the range of 60 to 100 Hz. The resulting composite response curve had a slight mid-bass emphasis, but its ±4-dB variation from 28 to 20,000 Hz represents excellent speaker performance by any standards.
The tweeter dispersion was very good up to 10,000 Hz or higher (about 4 dB maximum difference between the response curves measured on axis and 45 degrees off axis), but the curves diverged sharply at higher frequencies, with about 17 dB difference at 16,000 Hz. Some of the benefits of the Time/ Energy design concept were demonstrated by the speaker's good group-delay characteristic. The T/E 320 impedance is rated at 4 ohms, and our tests validate this figure.
The T/E 320 is a relatively efficient speaker, especially for one using a non-vented enclosure. When we drove the speaker with 2.55 volts (equivalent to 90-dB SPL in the midrange) the woofer distortion was very low. At some frequencies, the low-frequency tone produced audible panel buzzing from the speaker, but the speaker's total output was very loud under these unusual conditions (and notably free of the usual bass harmonic distortions). We never heard it on music even when there was substantial deep-bass content.
The short-term power-handling ability of the EPI T/E 320 was tested with single-cycle tone bursts at frequencies of 100, 1,000, and 10,000 Hz. By displaying the driving pulse and the speaker's acoustic output (from our laboratory microphone) simultaneously on a dual-channel oscilloscope, we could determine its maximum output capability from the appearance of waveform distortion on the acoustic output (or on the amplifier output if it occurred there first). Sometimes the acoustic output of a speaker simply stops increasing with higher drive levels or rounds off gradually instead of "clipping," and this point is considered to be its maximum power capability for that frequency. Based on the T/E 320's rated 4-ohm impedance, the 100-Hz output rounded off at 190 watts input. Measurements at 1,000 and 10,000 Hz (midrange and tweeter operating frequencies) were limited by amplifier clipping.
The sound we heard from the EPI T/E 320 speakers was completely consistent with their measured characteristics (which is not necessarily true of all speakers we have tested). In our listening room they had a fine octave-to-octave balance and a sweet, smooth, and airy overall character, which included the modest' amount of bass emphasis that we have experienced from most speakers used in that room. In our listening tests we placed them several feet from the side walls and about 18 inches from the wall behind them.
What impressed us the most about the T/E 320 speakers was not one of their features or specifications, or even one of our measurements. We have tested and used a number of speakers that sound about as good as the T/E 320 (but very few that we would describe as unequivocally better). But most of these cost far more, usually from two to six times as much, as a matter of fact. There is nothing surprising about hearing excellent sound from a speaker costing from several hundred to a few thousand dollars, but we do not often enjoy this experience from a $250 speaker.
Nothing we heard from the EPI T/E 320 would have been inconsistent with the performance of some of the finest (and much more expensive) speakers. The several A/B comparisons we made were sufficient to make that point. This does not mean, of course, that the T/E 320 sounds "as good" as any or all of those speakers (how could one possibly quantify "goodness" in that way?), but simply that it is very much in their class, sonically speaking. That, we would say, represents quite an achievement for any $250 speaker.